Paint roller manufacturing typically involves multiple stages. By the late 1980s, and into the 1990s commercially viable methods of manufacturing thermoplastic paint rollers were developed. See, e.g., U.S. Pat. Nos. 5,195,242, 5,572,790 having a common inventor herewith. These patents describe continuous processes of manufacturing paint roller sticks. Sticks are several times the length of a finished paint roller. Thermoplastic paint rollers used heat or molten plastic materials in the process of manufacturing paint roller sticks. For example, many processes used molten polypropylene or molten polypropylene compounds with melting points in excess of 300 degrees Fahrenheit.
Sticks are typically 65 inches long when they come off a production line (e.g., as the end product of a continuous production line) at an elevated exterior temperature. For example, a stick may be cut from the output of a continuous processing line with an exterior temperatures that is greater than 90 degrees Fahrenheit, or greater than 100 degrees Fahrenheit, or greater than 110 degrees Fahrenheit. Internal components of the sticks may remain much hotter than the exterior temperature when cut.
After manufacture, the sticks are allowed to cool, harden and set over time. During the cooling, hardening and setting processes, the sticks shrink, often substantially, e.g., more than an inch, or more than 1.5 inches. Indeed, it is likely that the principal reason for the historical selection of 65 inches as the industry standard stick length is the ability to cut seven 9-inch paint rollers (which is a very popular size) therefrom, after shrinkage. After the sticks are hardened and set, and thus have shrunk, they are cut down to final paint-roller lengths. In an embodiment, a, typical paint roller length may be 3, 4, 6, 7, 9, 12, 15, or 18 inches long. Other lengths (e.g., metric lengths) may be used as well. As an illustration, a 65-inch stick that has hardened and set may have shrunk by well over an inch, but it can still be cut into to seven 9-inch paint rollers. Other typical stick sizes may be used (i.e., other than 65 inches) for making 9-inch or other roller sizes, however, all sticks are sized to allow for substantial shrinkage and result in waste in the cutting process.
Prior to the invention described herein it was well known to persons skilled in the art that cutting a paint roller stick into paint rollers of final length should not be done until all or substantially all of the (axial and radial) shrinkage has occurred. Thus, typically, final cutting of paint rollers would not be performed until the stick has hardened and set. For example, final cutting may be performed when the exterior surface of the stick has a temperature of less than 90 degrees Fahrenheit or less than 100 degrees Fahrenheit.